Topic 5A

Question 1

List the short term genetics applications

Answer 1

1. Hybridization & crossbreeding
2. Chromosome set manipulation/polyploidy
3. Sex manipulation
4. Sex reversal

Question 2

Hybridization & cross breeding

Answer 2

• Intraspecific (within own species)/Interspecific (b/w diff species)
• Combine favourable qualities from two genetically diff species (interspecific hybridization)
• Take advantage of hybrid vigour –> improved growth rates, manipulated sex ratios, improved flesh quality, ↑ed dz tolerance

Question 3

Chromosome sets manipulation/polyploidy

Answer 3

• More than two homologous chromosome –> polyploid
• Triploidy
• Apply thermal & chemical shocks to developing embryos
• Mostly done in molluscs
• Triploids are sterile –> more energy for growth process instead of maturation & reproduction

Question 4

Sex manipulation

Answer 4

• Develop complete/dominant male/female population or “super-male” genotype (YY)
• take advantage of sexually dimorphic characteristics –> control reproduction/prevent establishment of exotic species
• Monosex stocks –> considerable commercial benefits
  (e. g. male tilapia preferred for ↑er biomass –> female use more energy for repro.; monosex female trout & salmon grow better)

Question 5

YY = ‘super males’

Answer 5

1. Natural male = XY; natural female = XX
2. Offspring = XY/XX
3. Natural male (XY) convert to female when induced increased temperature (stress) during juvenile stage
4. Become female but with XY chromosome
5. Mate with XY; offspring = XX, XY, YY

Question 6

Sex reversal

Answer 6

• Super males mate with normal XX females –> produce all-male (XY) offspring
• XY males can be turned into phenotypic females –> use of sex hormones
• Inducing temperature at offspring, YY males become females
• Crossbreed super YY males & produced YY males (now female) –> whole population of YY male –> can mass produce

Question 7

List the long term genetic applications

Answer 7

1. Domestication
2. Selective breeding
3. Genetic engineering (lateral gene transfer)

Question 8

Domestication

Answer 8

• Wild fish move to aquaculture settings –> new form of selective pressure that may alter gene frequencies
• use established high performance domestic strains
• Domesticated broodstocks more cost-effective than wild broodstock
• Strain variation important –> strain effect on other genetic enhancement approaches

Question 9

Selective breeding

Answer 9

• ↑ growth rate/biomass
• Additive genetic variance –> ↑ survivability/growth rate, adaptable to env
• New traits –> disease/stress resistance, timing of maturity & flesh quality, specific pathogen free, enhanced feed utilisation

Question 10

Genetic engineering (lateral gene transfer)

Answer 10

a) Aquatic feed production
- Carried out to ↓ dependency on fishmeal & fish oil
- Improve terrestrial animal- & plant-based feed ingredients

b) Growth enhancement in fish
- Mainly done to transfer growth hormone (GH) genes
- Affects body composition, body shape, feed conversion efficiency, dz resistance, reproduction, tolerance of low O2 conc, swimming ability, predator avoidance
- Pleiotropic effects: one quality trait is inserted for improvement, another trait will be enhanced/eliminated

Question 11

General genetics applications

Answer 11

• Determine parentage for premium offspring in selective breeding
• Monitor genetic effects of aquaculture escapees on wild populations
• Conduct traceability aquaculture certification schemes
• Identify mislabelling & consumer fraud
• Diagnose dz